1. Field of the Invention
This invention relates to multihull sailboats; specifically those having a central main hull and an auxiliary side hull on either side of the main hull and referred to as a trimaran. More specifically, the present invention relates to a trimaran in which the width or beam of the vessel may be varied.
2. Description of Background Art
Single hull sail boats are conventionally equipped with a large, heavy keel extending downward from the bottom of the hull. A keel is required to counteract the tendency of a boat to roll (heel over) excessively about the longitudinal axis of the boat when it encounters heavy seas and/or stiff winds.
The large weight of the heel, concentrated at a posiion well below the hull of the vessel, lowers the center of gravity of the vessel. This provides a static righting force counteracting the tendency of the vessel to roll.
Typically, the keel of a sailboat has a broad flat shape, as viewed from the side of the vessel. The large surface area of the keel provides a substantial resisting force to rapid movement through water in a direction perpendicular to the surface. Thus, the keel provides a dynamic resisting force counteracting the tendency of the sailboat to rapidly heel over.
Trimarans avoid the requirement for a large and heavy keel by using auxiliary hulls or floats, one on either side of the main hull of the sailboat. The auxiliary hulls or floats are usually attached to the main hull by means of connecting crossarms transversely disposed between the main hull and each float. Typically, the floats are of an elongated shape, and in parallel alignment with the main hull of the sailboat, at equal distance on either side of the main hull. The transverse cross-sectional shape of both the main hull and the floats are so configured as to provide a hydrodynamically streamlined body, which may move longitudinally on the surface of water with a minimum amount of drag.
Auxiliary hulls or floats eliminate the requirement for a large and heavy keel as follows. The upwardly directed buoyancy force on a float, multiplied times the relatively long moment arm comprised by the distance between the float and roll axis of the main hull, provides a large torque ending to counteract excessive roll of the main hull in either a clockwise or counterclockwise direction.
The distance between the outer lateral edges of the floats of a trimaran is referred to as the beam of the vessel. A large beam typical for a trimaran is advantageous for sailing purposes, as has been described. However, the large beam can be disadvantageous when the boat is docking in crowded areas, or being transported by trailer. Accordingly, it would be advantageous to provide means for varying the beam of a trimaran.
A number of prior patents disclose a variety of structures for varying the beam width of a trimaran or other vessel. The following U.S. patents are typical of prior art disclosing variable beam width vessels:
Sanner, U.S. Pat. No. 4,286,534, Sept. 1, 1981, Trimaran Sailboat.
Woods, U.S. Pat. No. 1,683,276, Sept. 4, 1928, Boat.
Dornier, U.S. Pat. No. 2,271,065, Jan. 27, 1942, Fuselage for Hydroaircraft.
Robinson, U.S. Pat. No. 3,139,058, June 30, 1964, Multiple Hull Water Vehicles.
Miller, U.S. Pat. No. 3,925,837, Dec. 16, 1975, Boat Hull Construction.
Davy, U.S. Pat. No. 3,960,102, June 1, 1976, Trimarans.
Lindsay, U.S. Pat. No. 3,937,166, Feb. 10, 1976, Float Connection Assemblies for Multi-Hulled Boats.
Winch, U.S. Pat. No. 3,996,874, Dec. 14, 1976, Surface Craft.
Andersson, U.S. Pat. No. 4,392,444, July 12, 1983, High Stability Trimaran.
Thurston, U.S. Pat. No. 4,457,248, July 3, 1984, Multihull Vessels.
Typical prior art trimarans having a variable beam disclose the use of pivotable or hinged joints between the main hull, crossarms and floats of the vessel. The variable beam trimaran according to the present invention eliminates the requirement for such joints.